Hitherto, as a smelting method for nickel, a method in which a mat having a nickel grade of about 30% by mass is obtained by dry smelting of nickel sulfide ore and electric nickel is then produced by a chlorine leaching-electrolytic winning method.
In recent years, a high pressure acid leaching (HPAL) method using sulfuric acid has attracted attention as a hydrometallurgical method for nickel oxide ore. This method does not include dry treatment steps such as reduction and drying steps but includes consistent wet steps unlike general conventional smelting methods for nickel oxide ores, and it is thus advantageous in terms of energy and cost. In addition, there is an advantage that it is possible to obtain a sulfide containing nickel (hereinafter, also referred to as “nickel sulfide”) in which the nickel grade is improved to about 50% by mass. This nickel sulfide is produced as follows. A sulfide precipitate is generated by purifying the leachate obtained by leaching nickel oxide ore and then blowing hydrogen sulfide gas into the leachate in the sulfidization step to cause a sulfidization reaction. The nickel sulfide is recovered by subjecting the slurry obtained from the sulfidization reaction to a sedimentation separation treatment using a solid-liquid separation device such as a thickener.
The particle diameter of nickel sulfide to be precipitated and generated is in an appropriate range. When the particle diameter is too small, moisture contained in the sulfide powder that is pressed and dried after solid-liquid separation increases and the powder is cured, for example, during transportation after being pressed. In addition, the entire surface area of the powder increases, thus the porosity increases, the volume increases as compared to powders having a larger particle diameter even of the same weight, and the conveyance cost increases. Meanwhile, when the particle diameter is too large, the nickel concentration after the sulfidization reaction increases and the actual yield of nickel decreases.
However, in the related arts, a method for controlling the particle diameter of nickel sulfide to be obtained is not established in a method for obtaining nickel sulfide from an acidic solution of sulfuric acid containing nickel, and a method for stably producing nickel sulfide having a desired particle diameter is demanded.
Patent Document 1 discloses a method in which a complex salt solution of an ion of a base metal such as nickel is atomized by using a nebulizer so as to have a certain particle diameter, the complex salt solution of atomized base metal is brought into contact with or introduced into a reducing solution or reducing gas which reacts with this base metal to instantly reduce the particulate base metal complex salt to a metal, and the fine metal powder thus obtained is recovered. More specifically, this citation 1 discloses a method for controlling the particle diameter of the fine metal powder by changing the solution concentration of the metal complex and the diameter of the nozzle mesh which is attached to the nebulizer and controls the diameter of the droplet discharged from the nebulizer. However, in the case of applying this method to the hydrometallurgical method for nickel oxide ore, suspended solids contained in the leachate to be supplied to the sulfidization step become clogged in the pores of the nebulizer and this causes a decrease in the working rate of operation.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-75708